Best Friends & Batman
by onlymystory
Summary: Isaac and Stiles have been friends for a long time. See, Derek will always be Stiles' mate. Scott will always be Stiles' oldest friend. But Isaac's the one who knows why he sometimes smiles as he kills an enemy. Why the song of blood lust is so tempting. And why slaying bad guys will make you both hungry and horny. Today is no exception.


**I've been playing around with this story for a while and finally got around to finishing it.**

**As usual, a reminder that this is part of the BAMF!Stiles series that is related only because each one features a BAMF!Stiles, not because they are in the same 'verse. However, this particular story does belong in the same verse as "The Alpha's Second". You do not need to read that one first to read this story, but if you like this one, you should like it as well.**

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Best friends are a funny thing. Up until high school—and sometimes even through high school—it seems like the kid who shoves a grape up his nose so you don't have to go to the nurse alone in second grade will be your best friend forever.

But that's just not really how it works.

High school and the years after that change people. Sometimes you keep changing, but usually you start getting a better feel for who you'll be and all that jazz around that time.

Stiles grew up assuming Scott would be his best friend until the day they died. Which for a while there seemed like it might be happening sooner rather than later. In some ways, Scott's still his absolute closest friend. He's the first person Stiles called when Derek proposed—both marriage and the role of Alpha's second—and he's still the first person who gets to talk to him on anniversaries to do with his mom. Scott's always been able to be there while Stiles cries, then help him get his game face on to spend the rest of those days with his dad. Nowadays, Derek comes in at the end and comforts him. But Stiles still turns to Scott first.

But in the day to day stuff, the coming at things from the same perspective, the decisions they make and the things they can live with…that's changed a lot over the years.

Now his best friend is Isaac Lahey. And if you'd asked Stiles to explain how that would happen back in high school, he probably would have laughed in your face.

It wasn't easy.

First they fought over Scott. There was the lingering knowledge that both of them had harbored long crushes on Lydia Martin. Stiles hated Isaac for getting to actually call Derek his alpha, that Derek wanted Isaac so much he chose him first. (Not that Stiles brought that up around Jackson, since now that he was fully pack, still took a while to get over his insecurity issues over not being wanted). Isaac in turn spent a decent amount of time hating Stiles for being the one Derek trusted most.

To be perfectly honest, Stiles isn't sure when exactly their issues went from hatred to the Thelma & Louise thing they've got going on now. (Thanks so much to Erica for the nickname).

He wonders sometimes if it was somewhere after the alpha pack, when there were little skirmishes throughout senior year that kept getting worked out way easier than expected, and afterwards Stiles and Danny were always the ones wired and awake, so they'd convince Derek to buy burgers at the 24hour drivethru and sprawl out in the loft living room with Isaac and Derek and watch old TV shows.

Stiles was already fucking Derek at that point. And really, fucking was the best word for it. They mostly had quick and usually rough we-didn't-die-this-time-and-wow-Faith-was-right-sl aying-makes-me-horny sex.

Those movie nights became weekends fixing up the house Derek had built on Hale land. Weekends became several days a week study sessions and training drills.

Stiles fell in love with Derek.

Derek fell in love with Stiles.

Stiles mostly missed it—he was kinda preoccupied—but Isaac and Danny fell in love around the same time.

And by the time he was a year away from graduating college at 21 (thanks AP classes), he'd realized he was roommates with his boyfriend (mate), and two friends, and that Isaac Lahey had somehow taken the spot of his best friend.

Stiles hasn't stopped maintaining that it's weirder that Derek and Danny are bffs on the level that he and Scott were pre-werewolf shenanigans.

They literally finish each other's sentences.

When they actually speak.

Seriously. It's fucking weird.

Anyway, the point is more that Isaac gets Stiles' darker side. So does Peter, but he's Peter so that only goes so far. Derek has a lot of anger and rage but he doesn't actually get to that cold anger, that point where you could kill anyone who hurt those you loved without remorse or a second thought. Stiles does. He has lines and if you cross them, he'll cross right back.

Which is why he and Isaac are currently standing just inside an abandoned warehouse outside of town, waiting on a rival pack to show up.

The interlopers trespassed into Beacon Hills a couple weeks ago without asking permission of his Alpha. They've been extended both an invitation and a demand to remedy that grievance. The plan was for Derek, Stiles, Erica, and Peter (the latter two are next on the list of who gets to go on enemy outings) to meet the pack tomorrow and inform that they must leave. If force is necessary, the Hale pack will use it.

No one is all that concerned either. After a decade of dealing with the supernatural, no one really bothers getting out of bed for anything less than a demon. Even the police force is trained in supernatural techniques. Half of them are also supernatural but that's beside the point. People cause problems for the pack, but it's dealt with away from town and everyone keeps their happy lives. Usually no one bothers with Beacon Hills anymore but someone always misses the memo.

Then Scott had come running into the house this morning with news that the trespassing pack had killed an eight year old boy. Snatched him out of his backyard, clawed him to death, and left specific markings on his body that indicated a challenge.

Peter was seeing red at that point—as tended to happen when someone hurt little kids—so while Boyd and Jackson calmed him down, Derek and Allison had quickly conversed. A move like that changed things.

When they were finished, Derek had calmly turned around and spoke in a low voice. "Stiles. Isaac. Take care of the problem."

Isaac and Stiles had turned as one to Scott.

There were rules to how they worked. Most of the time, Derek was the Alpha, but he'd become very good about talking things over with Scott first. In situations like this, Scott had to also give the order to let Stiles and Isaac take the rival pack down. Or whatever the enemy may be.

Okay so technically the rule was that Derek and Allison made decisions together because she'd turned the Argent name back into something to be feared _and_ respected, and Derek was actually pretty used to women taking leadership roles so working with Allison was pretty easy. Her approval on kills also meant other hunters couldn't come after them. They'd spent the rest of high school and a couple years into college with Allison & Derek just trying to figure out a way to put up with each other. Forget trust. Then another hunter family had come into town and tried bargaining with them. Allison had politely listened. One of the young male hunters in the family had looked at Erica and said, "Look, just let us take the bitch off your hands. Otherwise the rest of the animals will just breed her."

Allison shot him in the throat at point blank range and followed up with the hands down scariest lecture Stiles had ever seen from anyone at the matriarch and the hunters left in a hurry. The word quickly spread that you did not fuck with Beacon Hills.

Derek spent four hours making raspberry ganache filled cupcakes—Allison's favorite—the next day. They'd been friends ever since and a leadership duo that struck fear in a hell of a lot of hearts.

Anyway, the thing about Scott was that he still believed in the good of people. He still took the peaceful approach first, though he could tear an enemy apart just like the rest of them if necessary. Stiles and Isaac both trusted Scott for the final approval in missions like these. If he set them loose, it really was the only option. If there was a chance of redemption for their enemy, Derek, Allison, and some other combination of the pack went. Stiles or Isaac could still go, just not alone.

Stiles rarely saw that particular look on his best friend's face, but the fury in his eyes was barely held in check when he told them to go and not to leave any survivors. Not that he blamed Scott. The trespassing pack had gone after a child—an innocent ,human, and unrelated to the pack child—simply to make a statement.

The Hale pack wouldn't let them make a second one.

He'd allowed himself a momentary grin at the idea of what was to come before he'd gone to grab his things. Isaac followed Lydia & Danny so they could hide his scent when he and Stiles tracked the intruding pack.

It took maybe twenty minutes for them to be ready to go.

Now Stiles looks over at Isaac. "Ready?"

"Born ready," answers Isaac and Stiles grins in response. Isaac thinks the cheesy banter is just that—cheesy—but he does it anyway. "They're late."

"Rude," observes Stiles. Isaac blinks slowly, a sign that they aren't alone and Stiles imperceptibly stands more alert.

"You should learn better observational skills," says the Brimmel Alpha, as she steps from the shadows.

Stiles shrugs. "We understood your message easily enough. It seems you didn't get ours. Beacon Hills is closed to you and your pack. Get out."

"Now why would we do that?" drawls the Alpha. "This land is rich with history and magic. We want it. It'll be ours."

Isaac snorts. "Please don't finish that with 'it'll be our precious.'"

Stiles can't help his own bark of laughter at that.

One of the betas looks derisively at Stiles. "So it's true. The Hale alpha not only took a _human_ for his mate, but actually sends him out to fight his battles for him."

Isaac bristles more than Stiles does at that. Stiles has gotten used to the insults at this point. They come from ignorance and stupidity and are usually followed by the speaker's quick death.

The Brimmel pack Alpha ignores her beta, though the look on her face indicates she agrees with the assessment. "You've obviously come to negotiate. Speak your terms so that I may refuse. Our pack has years of experience and we are not bitten nor human. We'll take your land, whether you give it to us or are buried under it."

Isaac claps. "That was beautiful. No seriously, go on. Do you get all your speeches from Batman movie villains?"

The beta who insulted Stiles lunges at Isaac, snarling some nonsense. Isaac darts to the side, reaching a hand out as he does so. The werewolf ends up skidding out on the floor and Isaac tosses aside the bloody mass in his hands. "How many is that?" he asks in a bored tone.

Stiles glances behind him at the werewolf on the ground and verifies that his throat was in fact ripped out. "Sixteen." Derek kept making that threat—albeit with no real intent behind it—when they were younger that Isaac had wanted to see if he could do it. He and Stiles kept a tally.

Isaac stalks over and looks down at the body, his eyes beginning to get a far off look. He leans down, extends one claw and carves out a Joker like smile into the werewolf's face. "Not so serious," he says gleefully.

The motion is enough to wake the Alpha out of her shock. "We will destroy you both and leave your bodies in pieces on your mates' doorsteps." She beckons and the rest of her pack steps out of the darkness.

Stiles is getting tired of the bad speeches. Plus ten werewolves and an overly cocky Alpha is just the sad version of a baker's dozen. It'll be more work to bury this pack than to kill them.

"Yeah, whatever. Isaac, it's all you."

Isaac steps away from the dead werewolf to face the pack. The two of them fight seamlessly, with Isaac getting most of the kills. Stiles gets more battle time as a general rule. He's both the Alpha's second and the Alpha's mate, so it means he's often required to come along. But Isaac also has to be left behind a lot, because he crosses into this dark, crazed killer more easily than anyone is comfortable with. Even Isaac usually requests that he be left out of most battles. He's one of the best healers in the pack, and along with Scott and Melissa, usually takes care of any injuries afterwards. The kill…Isaac enjoys it far too much.

So when situations like this arise, Stiles and Isaac move like dance partners.

Isaac gets to fully unleash his demons.

Stiles uses his bat to make sure no one catches Isaac off guard. It's never happened yet, but Stiles always says better safe than sorry. He also finds a particularly joyful satisfaction in the sound of his iron bat cracking through bone.

He never said he was normal either.

The Alpha is the last to go down, as Isaac gouges into the skin over her heart. Stiles reaches down and pours concentrated wolfsbane into the opening. It will kill her before another minute passes. "Courtesy could have saved you so much trouble," he whispers as she dies.

Isaac returns to a couple struggling betas, bringing them to a quick death instead of a lingering one, before standing and glancing back at Stiles.

Stiles breathes heavily, one bloody hand wiping the sweat from his brow. It mostly trades one liquid for another but the gesture feels relieving. He turns to Isaac to see his best friend staring at him. Stiles always feels like these are the moments when death dances in Isaac's eyes.

Isaac takes a predatory step forward and Stiles sighs. It's always nicer when Isaac comes out of these trances on his own, but of course the entire point of the pair of them teaming up was for issues that needed this inhuman side of both of them. Stiles simply balances better. He's long suspected it's because he doesn't have two sides of himself, warring with each other in these moments. Stiles reaches for the duffle he brought in, shoving the body of a dead werewolf off it first, and digs around while Isaac stalks him.

Sometimes the movement makes Stiles miss the early days when Derek's alpha power was still overwhelming in a fight. The way it made Derek stalk Stiles like prey until they both ended up rutting on the floor, slick with blood and the thrill of victory on their tongues, was still one of Stiles' biggest turn ons. He didn't have any desire to do that with Isaac and Derek wasn't nearly as bloodthirsty these days. Stiles considers briefly that he and Derek could probably go on a normal hunt and relive the old days. Derek's usually accommodating to Stiles' fantasies.

While he ponders, Stiles grabs a small bottle from the bag and squirts the contents over his shoulder at Isaac.

Isaac howls in pain at the liquid wolfsbane. His beta eyes flash, claws spring out, and within another moment he's shifted to his wolf form before going back to human.

Stiles takes out his other bottle—a healing solution that Lydia had concocted some time ago—and douses Isaac fully, rinsing away the effects of the wolfsbane. "You back?" he asks.

Isaac nods. "Give me a minute," he croaks out, the monkshood still having an effect.

"Fine." Stiles busies himself by cleaning his bat, wiping it down and then scrubbing it with salt and mountain ash to keep the effects strong.

The wolfsbane he'd thrown was designed to trigger the shift. Once Isaac's full wolf was released, it always brought him back to sanity, and that in turn kept Stiles safe. He'd only had one instance when he'd actually had to fight Isaac off first. Neither wanted to repeat it.

Eventually Isaac recovers. "Are we cleaning this up? "

"Argent's got it covered. Guess they were tied to a hunter clan and Allison told Chris he had to take care of clean up and send their matriarch to her for instructions on how interactions with Beacon Hills will be held in the future."

"Let me guess, the clan isn't welcome within a hundred miles of Beacon Hills?" Isaac grins. He's certainly been on the receiving end of a furious Allison Argent years ago, but that was nothing compared to how the huntress was now. People called Victoria Argent terrifying. She didn't hold a candle to Allison.

The legends were that no one lived long enough to cross Allison twice.

Whenever someone told her that, Allison would smile sweetly, in that Disney princess way she had and say, "Oh sweetie. Legends are based on rumors. Why would I let you cross me even once?"

Usually internal organs ended up on the ground after that.

"More like two hundred," laughs Stiles. He zips the bag shut and tosses it to Isaac to carry out, texting Chris as they go.

"Wanna get Chinese food?" asks Isaac on the way home.

Stiles make the appropriate turn for their favorite place. "I feel like double the rangoons this time around. Slaying makes me hungry."

"And horny." Isaac laughs at him for bringing up Buffy references again. He's also probably laughing a little because they'll get back to the house, debrief everyone while eating, and then disappear into their respective bedrooms for the rest of the night.

Thank god Lydia learned a spell to soundproof the rooms.

Stiles doesn't deny it. He hasn't decided yet, but he's thinking he wants to ride Derek slowly tonight.

They fill the trunk with food for the entire pack. At home, Chris has already called Allison with confirmation of the bodies' disposal. Scott and Erica take the lion's share of the food to Boyd's truck—it seems the majority of the pack is crashing at Jackson & Lydia's tonight—and leave Isaac and Stiles to their mates.

Stiles quickly assures Derek that the job was done. After eating, Isaac elbows Stiles as they walk through the doorway.

"Twenty bucks says I can make Danny moan loud enough it breaks the spell's barrier." He jumps a little as Danny slides up behind him and grabs his ass.

Stiles would laugh but Derek's got one hand down the front of his pants and is turning them towards the opposite end of the hall. He yells back over his shoulder. "Double or nothing Derek screams my name before you can figure out where your dick goes."

Derek huffs a laugh into Stiles' shoulder as he bites at his neck.

Isaac takes the bet.

He wins.

It surprises no one.

Isaac always wins their bets. Stiles keeps taking them. It's what best friends do.

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**Notes:**

**Danny & Derek feel like their friendship is the easiest to understand. Certainly easier than the whatever the fuck relationship thing that is Jackson/Erica/Boyd. But because some people *cough* Stiles & Isaac *cough* don't seem to get it, here is their list.**  
**1) Neither of them feels a need to add commentary to every moment in life. Yes, Isaac is as bad as Stiles. **  
**2) People do not have ambiguous feelings towards either Danny or Derek. You love 'em, hate 'em, don't know 'em. That's it.**  
**3) They have not now or ever been in love with Lydia Martin and therefore the words "strawberry blonde" will not make them swoon. Also, we are not Victorian.**  
**4) They go along with the idiot schemes their boyfriends dream up because they love them. **  
**5) There was one night senior year when they were eating dinner at the Sheriff's and Isaac made peanut butter cookies (which Danny hates) and Stiles made chocolate chip cookies (which Derek hates) but they were both so proud of the effort that Danny & Derek took bites, grinned and said this was the best cookie ever, and then switched with each other under the table. They've never told their respective boyfriends the truth. It's easier to distract them and switch.**  
**6) Sometimes, Isaac shuts down after being in small spaces. Other times, Stiles still has panic attacks. They're rare and always away from any sort of dangerous situation—Stiles and Isaac have practiced too much control for anything else. But it's the hardest thing in the world for Derek to sit on the other side of the room and count for Stiles and not be able to touch him in those moments. For Danny, it takes all his willpower not to touch Isaac when he's panicking, because all Isaac senses is a threat. **  
**On those days, one of them goes and gets the case of beer, the other calls the Sheriff to sit with his mate while they recover. Derek drinks more of the beer and when all the bottles are empty, they throw them at the trees, screaming out their anger before sitting beside each other on the hood of the Camaro, knowing they share the same burning feeling in their chest. Then they go home to the men they love.**  
**7) They both know better than to put pineapple on a pizza. Gross. Really, this is the thing that bonds them for life.**  
**8) Lastly, neither Derek nor Danny says anything about the missions that Stiles & Isaac pair up on. They don't comment on the way either man comes back bloody and gleeful, or how they know that sometimes Isaac and Stiles get an unhealthy joy out of death. They just bring their boys back to the land of sanity together. **


End file.
